A portable hand-held cutting and sawing machine according to above is capable of very deep cuts by using two disk shaped cutting blades located close to each other. The material between the two close cuts, typically concrete, will either brake by it self during the cutting operation or will be broken away by the machine operator. This special method is referred to as “Cut and Break” and is described in U.S. Pat. No. 7,571,720 issued on Aug. 11, 2005 assigned to Husqvarna AB, titled “Cutting or sawing machine”, the disclosure of which is hereby incorporated by reference. This special method enables especially deep cuts, far deeper than the center of each cutting blade, like twice the diameter of the blades. Normally two cutting blades of the same size is used, but also one blade could be smaller. In a very special case it is possible to use a tool unit with only one cutting blade. The disk shaped cutting blades used are normally brazed to the corresponding blade driving members. Possibly they could be welded. The cutting blades are attached to flat annular surfaces of first and second driving members respectively, via brazed joints. The cutting blades are normally provided with outer segments comprising diamonds.
There is need to keep each cutting blade thin to keep each cut thin. Otherwise the power demand and thrust of the handheld machine would increase as well as the cost of the cutting blades. The cutting blade is manufactured from a specially high quality steel, e.g. hardened or cold rolled steel. However when the cutting blade is brazed there is a strong transmission of heat to the blade. The result is that the cutting blade looses a lot of its quality and strength. Therefore when subjected to hard cutting use it will lose some shape, not being fully flat any longer. The loss of shape will increase mechanical stress at the same time as the hardness and strength was already reduced by the heat of the brazing. There is also a stress concentration in the brazed or welded area of the disk where the thin blade is firmly connected to the thick driving member especially when the blade is prevented from heat expansion or bend. Further, the reliability of a welded joint along the welded area may not be ensured and minor defects may result in a failure of the welded joint. Cutting blades for a Cut-n-Break machine sometimes run under very difficult heat conditions as they are fully immersed in the material/concrete, so there is very little moving air available for air cooling. Instead cooling water supply is used, but can be forgotten or hindered. Brazing the disk shaped cutting blade and the corresponding blade driving member together tend to give high overall manufacturing cost for the tool.
In the light of the foregoing, there is a strong need for an improved tool unit and tool for this special type of cutting or sawing machines.